The invention pertains to a process for coating a substrate by means of a sputter cathode, which has a rotatable target carrier with a target in front of a magnet, in which process part of the target carrier projects into a sputtering chamber for the coating of the substrate and where another part projects into a target carrier coating chamber, so that the surface which has been coated in the target carrier coating chamber passes continuously through the sputtering chamber. In addition, the invention pertains to a coating system for the implementation of this process.
A process of the type described above is the object of U.S. Pat. No. 4,866,032. The component which serves as target carrier and target in the coating system described in this publication is designed as a circular disk, which rotates around a vertical axis; half of this component projects into a sputtering chamber, while the other half projects into a target carrier coating chamber. In the sputtering chamber, underneath the target, there is an array of magnets. A magnetron cathode is thus created there, which makes it possible to coat a large piece of foil economically. To be able to influence the properties of the coating system in spite of the use of one and the same target, two other targets are provided in the target carrier coating chamber, each of which has its own ion source. This makes it possible to deposit additional target material onto the main target in the target carrier coating chamber. As a result, this material can be atomized in the sputtering chamber together with the material of the main target, which is designed as a disk. In an alternative design, U.S. Pat. No. 4,866,032 states that a metal rod, the material of which can be vaporized to form a layer on the main target, can be provided in the target carrier coating chamber.
The sputtering process is the only coating process which makes it possible to produce usable layers economically on large surfaces. Only by this method is it possible to produce a layer of satisfactory uniformity over the large areas required for interference systems. For this reason, layer systems for architectural glass are produced almost exclusively by sputtering technology.
The sputtering process, however, suffers from serious disadvantages in comparison with other systems, especially thermal and chemical vapor deposition, arc vapor deposition, and electron beam vapor deposition. The disadvantages of the sputtering process include in particular the high price of the targets, the short service life of the targets, and the low degree of target utilization. The high price of targets is attributable to the cost of materials, to the cost of production, and to the cost of bonding. In many cases, the costs of production and bonding are much higher than the material costs. The service life of a flat target at the current sputtering rates is about 2 weeks. This means that sputtering systems must be shut down every two weeks and vented, so that the target can be replaced. An increase in the sputtering rates would shorten the periods between target replacements and therefore make little if any contribution to an increase in economy. In the case of flat magnetron cathodes, the degree of target utilization is currently about 25-30%. In the case of tubular cathodes, a target utilization of 70% can be achieved in practice.
The disadvantages of the sputtering process described above are also present in the coating system according to the above-cited U.S. Pat. No. 4,866,032. The system must be shut down at regular intervals so that the circular, disk-shaped, rotating target carrier with the target in the sputtering chamber and the additional targets in the target carrier coating chamber can be replaced with new targets or with the metal rod provided there. For this reason, continuous coating is possible only during a relatively short period of time.